Experimental studies in insect parasitism - VIII. Host reactions following artificial parasitization

Abstract

A method of artificial parasitization has been devised which allows eggs of insect parasitoids to be injected into any given species of host. By this means, eggs of an ichneumon fly, Nemeritis canescens, have been put into larvae of eight species of Microlepidoptera, none of which has ever been recorded as a host of that parasite. Three species encapsulated the parasite egg and prevented its hatching. In three species the egg hatched but the host reacted to the parasite larva: in two species by encapsulation, in one species by the blocking of its alimentary tract with melanin. Two species gave feeble reactions or none, and were partly or wholly susceptible to the parasite. The defence reactions of all these hosts to the same parasite took two principal forms: encapsulation and the deposition of melanin. Each species of host was capable of both forms, but each species reacted in a manner that was characteristic and peculiar to it. Nevertheless, hosts belonging to the same family reacted to the parasite in similar ways so that, within the limits of this preliminary survey, the defence reactions of a group of hosts to the same parasite reflect the relationships of the hosts.